#include <stdio.h>
//printf详解 http://blog.csdn.net/k346k346/article/details/52252626

int main(int argc, char const *argv[])
{
	int n,m;
	float s;

 //    n=1000000;
	// printf("%d\n",n*n);
	// return 0;

	while(scanf("%d%d",&n,&m)==2)
	{
		if(n==m&&n==0)
		{
			//end of prog
			break;
		}
		s=0;
		for (int i = n; i <= m; ++i)
		{
			if(i*i<0)
			{

			}
			else
			{
				s+=1.0/(i*i);
			}
		}
		printf("%.5f\n",s);
	}
	return 0;
}